1. Field of the Invention
The present invention relates to improvement and modification in a pulse light receiving time measurement apparatus and a distance measurement apparatus including the pulse light receiving time measurement apparatus.
2. Description of Related Art
Conventionally, a distance measurement apparatus has been developed for measuring a distance from the apparatus to a measuring object at a high speed by irradiating pulse light to the object and receiving reflected light from the object at a light receiving element to thereby measure a time from the irradiation of the pulse light to the reflected light's reaching at the light receiving element from the object (See Japanese Patent Application Laid-Open Publication No. 2005-214786).
Moreover, in recent years, there has been an increasing demand for three-dimensionally measuring, at a high speed, a distance to an object which ranges from a natural object with low reflectivity to a retroreflective member with high reflectivity.
The conventional metrology device which measures the distance by optically adjusting amount of light cannot deal with the above high-speed measurement of the distance to the object, and moreover, it has to have an optical receiver circuit which can detect amounts of light in a large range from extremely small to large.
However, an amplifier used for the optical receiver circuit generally has a dynamic range in which the maximum value is five to ten times as large as the minimum value. In order to measure reflected light from various objects form the natural object to the retroreflective member, the dynamic range in which the maximum value is over 1,000 times as large as the minimum value is needed. Therefore, the amplifier needs to be configured to have multiple stages in order to achieve such a large dynamic range.
However, addition of a pulse light receiving time measurement circuit to each of the multiple stages of the amplifier makes the scale of the circuit larger, which is disadvantageous.